Unit 3 A Human Form Function Cells metabolism

Unit 3 A Human Form & Function Cells, metabolism & regulation Regulation of fluid composition

Study Guide Read: w Human Prespectives 3 A/3 B Chapter 8 Complete: w RQ 10 -14 w AYK 5 -12

Structure of convolute the kidney Proximal Distal convolute tubule Capsule Cortex Renal corpuscle Medulla Pyramid Renal artery Renal vein Pelvis of ureter Ureter LS of KIDNEY Collecting duct Loop of Henle Peritubular capillaries A NEPHRON

Kidneys functions w Fluid balance Interdependent w Salt balance w Removal of wastes (especially urea) w p. H balance

Fluid balance w The kidneys play an important role in the homeostatic regulation of body fluids (both the amount and the composition). w If we become dehydrated the kidneys can increase the reabsorption of water from the filtrate, whilst also increasing the secretion of salt. If our tissue fluids are too dilute the opposite occurs.

Water reabsorption w 60 -70 % of water reabsorption occurs in the proximal convolute tubule*. w The remaining 30 -40 % is selectively reabsorbed in the loop of Henle, distal convolute tubule and collecting duct, depending on our state of dehydration. *How much water is reabsorbed at both stages depends on our state of dehydration i. e. less water is reabsorbed if our tissue fluid is dilute; more if we are dehydrated.

Urine formation There are three stages in urine formation: w Filtration (in the renal corpuscle) w Selective reabsorption (mainly in the proximal convolute tubule – some water and salts are reabsorbed in the loop of Henle and the distal convolute tubule) w Tubular secretion (in the proximal convolute tubule and the distal convolute tubule)

EM of a glomerulus D Gregory & D Marshall, Wellcome Images

Filtration Process Filtration Structure Renal corpuscle Substance Active/passive Filtrate Water Urea, Glucose, Amino acids, Vitamins, Salts (mainly sodium & chlorine) Passive (mass flow) Passive

Section showing Bowman's capsule, glomerulus and tubules Bowman's capsule Glomerulus Tubule Wellcome Photo Library

Selective reabsorption Process Structure Substance Active/passive Water (60 -70%) Passive (osmosis) Salts (60 -70%) Glucose (100%) Amino acids (100%) Vitamins (100%) All active Loop of Henle Water (25%) Na+/Cl- (25%) Passive (osmosis) Active DCT Water (5%) Na+/Cl- (5%) Passive (osmosis) Active Collecting duct Water (5%) Passive (osmosis) Reabsorption PCT

Tubular secretion Process Structure Tubular secretion PCT & DCT Substance H+ NH 4+ (ammonium) Creatinine Toxins Drugs Neurotransmitters Active/passiv e Active

Selective water The second reabsorption stage of water reabsorption is important if we become dehydrated. It can be divided into two phases (though both are interdependent). 1. The first phase involves the reabsorption of salt under the influence of the hormone aldosterone. 2. The second phase involves the reabsorption of water under the influence of the antidiuretic hormone (ADH).

Reabsorption of salt under the influence of aldosterone Ø Stimulus Decreased blood volume → reduced blood pressure Ø Receptor Baroreceptors in Renal artery

Ø Transmission Several chemical messengers ending with release of aldosterone from the adrenal cortex Ø Effector Sodium pumps in DCT and loop of Henle Ø Response Sodium reabsorbed increasing ion concentration in interstitial fluid (creates osmotic gradient)

Aldosterone stimulates sodium pumps Na+ Na+ High Na+ concentration In tissue fluid Low Na+ concentration In filtrate

Negative feedback loop Decreased blood volume Baroreceptors in Renal → reduced blood pressure artery Stimulus Receptor Creates osmotic gradient Feedback End-product is aldosterone from adrenal cortex Control centre Response Sodium reabsorbed Effector Sodium pumps in DCT and loop of Henle

Reabsorption of water under the influence of antidiuretic hormone Ø Stimulus Decreased blood volume → reduced blood pressure → increased osmotic pressure Ø Receptor Osmoreceptors in hypothalamus thirst reflex) → (activates

Ø Transmission nerve signal to posterior pituitary gland ADH released into bloodstream Ø Effector DCT and collecting duct Ø Response Increases permeability of above structures water (approx 10%) reabsorbed

ADH increases permeability of tubule Relatively dilute filtrate Water leaves the filtrate by osmosis Relatively concentrated tissue fluid

Negative feedback loop Decreased blood volume → reduced blood pressure → increased osmotic pressure Osmotic pressure maintained or reduced Feedback Stimulus Osmoreceptors in hypothalamus Receptor ADH from posterior pituitary gland Drink Thirst reflex Control centre Water reabsorbed Response Increases permeability of DCT and collecting duct Effector DCT and collecting duct

Deamination Definition - The stripping of nitrogen from amino acid and nitrogen bases (RNA) Deamination occurs in the liver → ammonia + organic compounds for w Amino acid respiration w Ammonia (very toxic) + CO 2 → urea (H 2 NCONH 2)

Nitrogen Wastes Nitrogen compound Source Amount Relative Toxicity Urea Amino Acids 21 g/day Moderate Creatinine Muscle metabolism 1. 8 g/day High Uric acid RNA 480 mg/day Weak